1. Field of the Invention
This invention relates to an improved method of application of Minoxidil to stimulate hair growth by means of iontophoretic transport to the hair follicle after converting Minoxidil to an ionic form.
2. BACKGROUND OF THE INVENTION
The patent literature is replete with compositions and processes for stimulating mammalian hair growth and/or keratin formation. Of these, Minoxidil (6-piperidino-2,4-diaminopyrimidine-3-oxide) is a drug which has been found to be useful in promoting hair growth. Minoxidil is normally applied as an active ingredient topically to the area where hair growth is desired. U.S. Pat. No. 4,970,063 describes and defines compositions and methods using what is defined as "Minoxidil," said patent being incorporated herein by reference. Other U.S.A. patents which teach the use of Minoxidil for hair growth are U.S. Pat. Nos. 3,461,461; 3,910,928; 4,139,619; and 4,596,812. It is believed that Minoxidil promotes hair growth after diffusion to the hair follicles. The precise site and mechanism of action have not as yet been elucidated.
Although Minoxidil is effective in promoting hair growth after it reaches the hair follicle, the clinical efficacy of topical application is limited by low water solubility and by the fact that the outer layers of skin are an effective barrier to penetration of polar molecules such as Minoxidil.
The technique of iontophoresis employs a small electric current to transport ionic drug compounds into the skin or other tissue. Iontophoresis is believed to increase drug entry through so-called "shunt pathways" provided by hair follicles and sweat glands. Since hair follicles are a major pathway for iontophoretic drug delivery, iontophoresis is potentially the ideal method of administering Minoxidil to the hair follicles.
Water is the preferred solvent for use in iontophoresis. Minoxidil itself has a low solubility in water and, because it has no net ionic charge, does not migrate in an iontophoretic field. In fact, due to the dipolar nature of Minoxidil, there is some evidence that the iontophoretic field inhibits even the passive migration by electro-osmosis often observed with non-charged compounds in electric fields.
Thus, although Minoxidil is effective in promoting hair growth after it reaches the hair follicles, presently there has been no therapeutic delivery system that utilized a transport mechanism other than passive diffusion in its attempt to deliver Minoxidil across the skin's membrane barrier to the hair follicle.